#define _CRT_SECURE_NO_WARNINGS 1

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* pruneTree(TreeNode* root) {

        if (root == nullptr) return nullptr;

        root->left = pruneTree(root->left);
        root->right = pruneTree(root->right);

        if ((root->left == nullptr && root->right == nullptr) && root->val == 0)
        {
            //delete root;
            root = nullptr;
        }

        return root;
    }
};


/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
    long tmp = LONG_MIN;
public:
    bool isValidBST(TreeNode* root) {
        if (root == nullptr) return true;

        bool left = isValidBST(root->left);
        if (left == false) return false;
        bool cur = false;
        if (root->val > tmp)
        {
            tmp = root->val;
            cur = true;
        }
        if (cur == false) return false;
        bool right = isValidBST(root->right);

        return left && right && cur;
    }
};